This invention relates to a temperature control system, for an internal combustion engine, having several different temperature control devices rendered operable as needed to maintain the engine temperature at a preselected desired level in the presence of widely varying external and load conditions.
Internal combustion engines used in trucks may have three separate controls to keep the operating temperature constant at an optimum point. A thermostat or flow control valve is usually installed in the engine block to sense or monitor the temperature of the coolant in the engine jacket, which coolant is circulated around the jacket by a coolant or water pump, and to divert a larger and larger amount of the coolant from the jacket to the truck's radiator to dissipate the engine heat as the coolant temperature rises through a relatively small temperature range. At that time no appreciable air is passing through the radiator but the total volume of coolant available to absorb the heat from the engine has been increased. If the coolant temperature continues to increase even with the thermostat fully open and with all of the coolant being circulated through the radiator, controllable radiator shutters will now become operable. These shutters are like venetian blinds and are positioned in front of the radiator. They may be of the variable opening type or the on-off type and are normally closed so that no air can be drawn therethrough and to the radiator. A separate temperature sensor controls the operation of the radiator shutters and they will be opened by the sensor if the engine temperature exceeds the desired level after the thermostat is fully opened. With the shutters open, ram air is allowed to impinge on the radiator to effect cooling of the coolant circulating through the radiator and engine block. Ram air is the effective air that, due to the truck's velocity, strikes the radiator. Of course, if the truck is stationary there would be no ram air.
If the load on the engine or external conditions, such as the outside ambient temperature, causes the coolant temperature to continue rising even with the thermostat and shutters fully open, a third temperature sensor will control the operation of a variable speed fan drive to pull outside air in through the shutters and then through the radiator to effect cooling of the coolant, the amount of air blown through the radiator, and hence the amount of heat dissipated, being proportional to the fan speed. It is this third temperature control device that will be capable of providing as much cooling to the coolant as needed to keep the coolant temperature at the required level for optimum engine performance. Moreover, by setting the fan speed only as high as necessary to maintain the desired optimum engine temperature, energy will be conserved.
It is of utmost importance that the three temperature control devices function in the proper sequence. For example, if the fan is operated before the shutters open a vacuum is created and the air flow becomes stalled, producing a very noisy condition. As another example, if the thermostat fails to open but the shutters and fan are rendered operable, no coolant flows to the radiator and the shutters and fan become ineffective. Unfortunately, in the past it has been extremely difficult to obtain the correct sequential operation of the thermostat, shutters and fan drive. Since three separate sensors are needed, whenever one of the sensors drifts out of calibration the required operating sequence will be disrupted. Each of the sensors, and the actuator that it controls, has a characteristic operating range and hysteresis which is extended further by reasonable manufacturing tolerances. In order for the control devices to work in the correct sequence, a rather wide total control range results. Engine temperature, allowed to vary over such a wide range, becomes dependent on such factors as load and ambient conditions. This wide temperature variation is not desirable due to its effects on engine efficiency and engine life.
The present invention constitutes an improvement over these prior engine temperature control systems by ensuring the proper sequential action of the coolant flow control valve, the radiator shutters and the variable speed fan drive. Moreover, the invention achieves a desirable reduction in the operating temperature range, namely closer temperature control to within narrow limits, resulting in higher efficiency and longer engine life.